Engineering Highly Homogenous Tetravalent IgGs with Enhanced Sperm Agglutination Potency

Abstract

Millions of women avoid using available contraceptives and risk unintended pregnancies every year, due to perceived and/or real side-effects associated with the use of exogenous hormones. Naturally occurring anti-sperm antibodies can prevent fertilization in immune infertile women by limiting sperm permeation through mucus, particularly multivalent antibodies such as sIgA that offers robust agglutination potencies. Unfortunately, sIgA remains challenging to produce in large quantities and easily aggregates. Here, we designed two tetravalent anti-sperm IgGs with a Fab domain previously isolated from an immune infertile woman. Both constructs possess at least 4-fold greater agglutination potency and induced much more rapid sperm agglutination than the parent IgG while exhibiting comparable production yields and identical thermostability as the parent IgG. These tetravalent IgGs offer promise for non-hormonal contraception and underscore the multimerization of IgG as a promising strategy to improve existing mAb therapeutics.Globally, over 40% of all pregnancies are unintended, which creates an enormous burden on healthcare systems.[1] For instance, in the U.S., nearly half of all pregnancies are unintended, resulting in an annual burden in excess of $20 billion per year.[2,3] Despite the availability of cheap and effective contraceptive methods, many women are dissatisfied with available contraceptive methods, particularly due to real and/or perceived side-effects associated with the use of exogenous hormones, including increased risks of breast cancer, depression, prolonged menstrual cycle, nausea and migraines.[4,5] Many women are also restricted from using estrogen-based hormonal contraceptives due to medical contraindications.[6-8] These realities strongly underscore the need for convenient non-hormonal contraceptives.Unfortunately, few options are currently available.An effective non-hormonal contraceptive mechanism already exists in nature: anti-sperm antibodies (ASAs) in infertile women, particularly polyvalent immunoglobulins such as IgA, can arrest highly motile sperm in mucus and prevent sperm from permeating through mucus and reaching the egg. [9,10] At high sperm concentrations, ASA can agglutinate sperm into clusters that are too large to permeate through mucus. [11] At lower sperm concentration, ASA can also immobilize individual spermatozoa in mucus via multiple low affinity Fc-mucin bonds between sperm-bound ASA and mucins. [12,13] Vaginal delivery of ASA that sustains pharmacologically active doses of ASA in the female reproductive tract can make possible both consistent contraception, and rapid reversibility. Indeed, vaginal delivery of sperm agglutinating ASA exhibited considerable contraceptive efficacy in a rabbit model, reducing embryo formation by 95% in the highly fertile rabbit model. [14]